Polysilicon fuses (or “polyfuses”) are used in semiconductor devices or packages due to their ability to be blown without an opening, which otherwise allows fused by-products to escape. Polysilicon fuses can thus be used for trimming during wafer sorting, final testing, and in other customer applications. Like traditional fuses, polyfuses can be affected by the high currents of electrostatic discharge (ESD) and electrical overstress (EOS) events.
In semiconductor circuit applications, polyfuses may be harmed by both undervoltage and overvoltage events. Generally, polyfuses have a polysilicon layer and a silicide layer on all or part of the top of the polysilicon layer. In an ESD event, high current flows through the polyfuse, increasing its temperature and melting the silicide and/or polysilicon, which can disable or blow the fuse. Additionally, the polyfuse may be rendered useless by current levels that do not blow the fuse, but merely increase the resistance of the fuse silicide. In these events, the intended drive circuit supplies sufficient current to heat and melt the silicide and polysilicon layers and blow the fuse, thus rendering the polyfuse useless.